640654360021 has 4 divisors (see below), whose sum is σ = 689935464652. Its totient is φ = 591373255392.

The previous prime is 640654359997. The next prime is 640654360063. The reversal of 640654360021 is 120063456046.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 142057379025 + 498596980996 = 376905^2 + 706114^2 .

It is a cyclic number.

It is not a de Polignac number, because 640654360021 - 2²⁵ = 640620805589 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640654360121) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 24640552296 + ... + 24640552321.

It is an arithmetic number, because the mean of its divisors is an integer number (172483866163).

Almost surely, 2^640654360021 is an apocalyptic number.

It is an amenable number.

640654360021 is a deficient number, since it is larger than the sum of its proper divisors (49281104631).

640654360021 is a wasteful number, since it uses less digits than its factorization.

640654360021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49281104630.

The product of its (nonzero) digits is 103680, while the sum is 37.

The spelling of 640654360021 in words is "six hundred forty billion, six hundred fifty-four million, three hundred sixty thousand, twenty-one".